A high-frequency, in particular, THz frequency band can be applied in various fields including imaging, spectroscopy, biochemical detection, astronomy, wideband communication, and the like. There is a trend that a concern about the THz frequency band gradually increases and a research for implementing a THz system based on a semiconductor device having advantages including a small size, low cost, low-power driving, and the like is in progress.
As a component that plays an important role in the THz system, an oscillator is provided. This is used as a signal source of a transmitter or a local oscillator in a heterodyne structure. In particular, since there are a lot of difficulties in implementing the oscillator that operates in a high frequency band, a research for enhancing performances of the oscillator, such as an operating frequency, output power, phase noise, and the like is in active progress.
The existing oscillator having a common-emitter cross-coupled structure requires a semiconductor device and inductance and capacitance (LC tank) having a significantly small size in order to an oscillation signal at a high frequency.
However, there is a physical limit in decreasing sizes of the components and since an oscillation condition is not met, the oscillator may not oscillate.
US Patent Publication No. US 2008-0290957 discloses contents in which an oscillator having a common base structure and an oscillator having a common emitter structure are compared with each other, but does not disclose a structure in which an emitter and a collector are cross-coupled.